Information needed on QOS Traffic Shaping

[Benso2013]

I've been reading up on Cisco QOS and reviewing some sample configurations. I've noticed that some people configure it on the Router and some configure in on the switch. What are the advantages of doing it on either device?  

[Alan Dunne]

Hi,

We mark traffic (set the dscp value) at the perimeter of the network, the closest point to the client.  Then as packets traverse the network we prioritize at each switch or router hop.

By marking the traffic at the edge, it allows shaping policies to be implemented immediately, before the packet even leaves its first switch hop.  The downside of this approach is more configuration points in your network.

Marking the traffic at the router would potentially leave the initial communication from the client to router in a "best effort" scenario, potentially being dropped along the way.

When marking the traffic it is possible to attach a policy to either physical interface or virtual.  Attaching the policy to a vlan interface should consume less resources.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Generally, QoS is used to manage congestion, which can happen on either a switch or router.  However, as routers often have LAN links on "inside" and WAN links on "outside", with the latter often having much less bandwidth than the former, the latter is also much more likely to congest so you'll often see QoS implementations there before you'll see them on switches.